1. Field of the Invention
This application relates to measuring devices, and more particularly to articulated spatial coordinate measuring machines.
2. Description of the Related Art
Portable coordinate measurement machines (PCMMs) such as articulated arm PCMMs can be used to perform a variety of measurement and coordinate acquisition tasks. In one common commercially-available PCMM, an articulated arm having three transfer members connected by articulating joints allows easy movement of a probe about seven axes to take various measurements.
For optimal precision and accuracy of the measurements generated by a PCMM, it must initially be calibrated to account for any manufacturing variations in the components of the PCMM itself. In one method, a portable coordinate measurement machine would be calibrated by using the PCMM to measure one or more length artifacts such as bars of precisely known dimensions. By using a PCMM to measure lengths of a length artifact having precisely known dimensions, position data obtained by the PCMM could be analyzed, to calibrate for errors in the PCMM.
In addition to the PCMM itself, when a probe is first connected to a PCMM, the probe itself must be calibrated for the specific PCMM. Each type of probe has nominal data that describe parameters of the probe, such as, for example, length, offset, category, type, capacity, features, etc. The nominal data for the probe is typically provided on a separate storage media such as a disk, memory key, hard disk on a computer, etc. The nominal data is often shipped along with the probe. When the probe is calibrated to the PCMM, the nominal data is used as a starting point for calibration. Therefore, matching the probe with the corresponding nominal data is essential for accurate calibration. Because nominal data is often contained in a separate media, associating the probe with the appropriate nominal data during the calibration process can prove to be difficult, particularly when probes are used with multiple PCMMs.
Further, each probe is typically calibrated once for each different PCMM that it is used on. That is, the probe's calibration data is unique to the particular probe and the PCMM. As with nominal data, the probe's calibration data is also typically stored in media different from the probe, such as, for example, a memory key, hard disk on a computer, storage area located on the PCMM, etc. When a particular probe that is already calibrated to the PCMM, for example, is reattached to the PCMM, the PCMM has to obtain the corresponding calibration data to accurately use the probe. Therefore, it is important that the calibration data that is generated for a probe is matched to that particular probe. Current PCMMs use identification resistors located on the probes to identify the probes such that the PCMM can obtain the corresponding calibration data from the different storage media. However, identification resistors typically contain enough information to only identify probes by type or category. As such, using the probe identification resistors to match the calibration data with the corresponding probe has shortcomings. For example, associating a particular probe with calibration data becomes extremely difficult in settings where multiple probes of the same type and/or category are used because identification resistors do not distinguish between different probes of the same type and/or category. Therefore, solutions that address these and other deficiencies are desired.